Chapter 24 / High-Level Visual Processing: From Vision to Cognition 575
Figure 24–9 Familiarity with particular complex objects
leads inferior temporal neurons to respond selectively for
those objects.(Reproduced, with permission, from Logothetis
and Pauls 1995. Copyright © 1995 Oxford University Press.)
A.Monkeys were trained to recognize a randomly bent wire
from a set of two-dimensional views of the wire. The wire form
was rotated 12° in successive views. Once recognition perfor-
mance was stable at a high level, recordings were made from
neurons in the inferior temporal cortex while each view was
presented. Peristimulus time histograms show the responses
of a typical neuron to each view. This neuron responded selec-
tively to views that represented a small range of rotation of the
object.
B.When the same neuron was tested with two sets of stimuli
that were unfamiliar to the monkey, it failed to respond to any
of these stimuli.
A 熟悉的目标 B 不熟悉的目标
–168° –120° –108° –96° –84° –72°
–60° –48° –36° –24° –12° 0°
800 毫秒
60 脉冲数/秒
下颞皮层
activity in the prefrontal cortex encodes visuospatial
information as well as information received from other
sensory modalities. Delay-period activity in the infe-
rior temporal cortex also appears to be closely attuned
to visual perception, for it encodes the sample image,
but can be eliminated by the appearance of another
image.
In the prefrontal cortex, by contrast, delay-period
activity depends more on task requirements and is not
terminated by intermittent sensory inputs, suggest-
ing that it may play a role in the recall of long-term
memories. Experiments by Earl Miller and colleagues
support this view. In these experiments, monkeys were
trained to associate multiple pairs of objects. They
were then tested on whether they had learned these
pairwise associations, using the following procedure.
First, a single (sample) object was presented; then,
after a brief delay, a second (test) object appeared. The
monkey was instructed to indicate whether the test
object was the object paired with the sample during
previous training.
There are two possible ways to solve this task. Dur-
ing the delay, the animal could use a sensory code and
keep a representation of the sample object online until
the appearance of the test object, or it could remem-
ber the sample object’s associate and keep information
about the associate object online in a “prospective
code” of what might appear as the test object. Remark-
ably, neuronal activity appears to transition from one
to the other during the delay. Neurons in the prefron-
tal cortex initially encode the sensory properties of the
sample object—the one just seen—but later begin to
encode the expected (associated) object. As we shall
see, such prospective coding in the prefrontal cortex
may be the source of top-down signals to the inferior
temporal cortex, activating neurons that represent the
expected object and thus giving rise to conscious recall
of that object.
The relation between long-term declarative mem-
ory storage and visual processing has been explored
extensively in the context of remembered associations
between visual stimuli. Over a century ago, William
James, a founder of the American school of experimen-
tal psychology, suggested that learning visual asso-
ciations might be mediated by enhanced connectivity
between the neurons encoding individual stimuli. To
test this hypothesis, Thomas Albright and colleagues
trained monkeys to associate pairs of objects that had
no prior physical or semantic relatedness. The monkeys
were later tested while extracellular recordings of neu-
rons in the inferior temporal cortex were made. Objects
that had been paired often elicited similar neuronal
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